Separating the surface and giving it different colors is relatively easy using split line and assigning different colored appearances to the split surface. The hard part is determining the curve(s) that the split line should be based on. Depending on how you are doing the wear measurements, you may be able to pre-process the measurements to define something similar to iso-lines (where wear measures change beyond a tolerance) and use that data to create the curves.
I was thinking of creating/drawing some sort of grid on the metal plate, which I can easily reproduce in a 3D model. I think the iso-lines should be a good way to represent the wear on different parts on the steel plate!
I have a material I use that changes color, it's just a 1 pixel wide gradient fill from black to brown.
You could make a bitmap that has a different colour for each level instead of a smooth transition and then project it onto your surface perpendicular to your wear pattern. Then when viewed from above you would have a colour related to the height